The aim of this proposal is to compare two state-of-the-art models for treating substance abuse in homeless people who are dually diagnosed with severe mental illness and substance use disorders. The project will focus on homeless women and minorities in Washington, D.C. The New Hampshire-Dartmouth Psychiatric Research Center, in conjunction with Community Connections, the largest service provider for the least-served sector of Washington, D.C., has designed two distinct models of intensive case management to provide comprehensive treatment for homeless dually diagnosed clients. In the Integrated Treatment model (IT), case managers provide comprehensive substance abuse treatment services in addition to mental health services. In the Parallel Treatment model (PT), case managers provide identical mental health services but link clients to local substance abuse providers and support and monitor their progress closely. This proposal will allow Community Connections to expand the already existing IT and PT programs so that 200 additional homeless dually diagnosed clients can be randomly assigned to one of the treatment models. The first goal of the project is to expand and maintain the IT and PT models. A second goal is to conduct a careful evaluation of the implementation and outcomes of intensive case management services through the two models. Objectives are: 1) To test our hypothesis that IT will be more effective than PT in ameliorating three critical problems for the dually diagnosed that define our primary outcome domains: abuse of alcohol and other drugs; housing instability and homelessness; drug-abusing social networks; 2) To examine whether clients who achieve good outcomes in the primary domains will also improve in traditional outcome areas such as institutionalization, psychiatric symptoms, functional status, and quality of life; 3) To examine the qualitative characteristics of homeless dually diagnosed clients' social networks and to understand through ethnography both how these clients make the decision to give up substance abuse and the role that changing social networks play in this process. The third goal is to examine the reliability and validity of instruments used to assess and monitor substance abuse among dually diagnosed clients.